Before his three-hour neck surgery for herniated disks in December, Peter Drier, 37, signed a pile of consent forms. A bank technology manager who had researched his insurance coverage, Drier was prepared when the bills started arriving: $56,000 from Lenox Hill Hospital in Manhattan, $4,300 from the anesthesiologist and even $133,000 from his orthopedist, who he knew would accept a fraction of that fee.

He was blindsided, though, by a bill of about $117,000 from an "assistant surgeon," a neurosurgeon based in Queens, N.Y., whom Drier had never met.

"I thought I understood the risks," Drier, who lives in New York City, said later. "But this was just so wrong - I had no choice and no negotiating power."

Drive-by doctoring

In operating rooms and on hospital wards across the country, physicians and other health providers typically help one another in patient care.

But in an increasingly common practice that some medical experts call drive-by doctoring, assistants, consultants and other hospital employees are charging patients or their insurers hefty fees. They may be called in when the need for them is questionable. And patients usually do not realize they have been involved or are charging until the bill arrives.

The practice increases revenue for physicians and other health care workers at a time when insurers are cutting down reimbursement for many services. The surprise charges can be especially significant because, as in Drier's case, they may involve out-of-network providers who bill 20 to 40 times the usual local rates and often collect the full amount, or a substantial portion.

"The notion is you can make end runs around price controls by increasing the number of things you do and bill for," said Dr. Darshak Sanghavi, a health policy expert at the Brookings Institution until recently. This contributes to the nation's $2.8 trillion in annual health costs.

"This has gotten really bad, and it's wrong," said James Donelon, the Republican insurance commissioner of Louisiana. "But when you try to address it as a policymaker, you run into a hornet's nest of financial interests."

In Drier's case, the primary surgeon, Dr. Nathaniel Tindel, had said he would accept a negotiated fee determined through Drier's insurance company, which ended up being about $6,200. (Drier had to pay $3,000 of that to meet his deductible.)

But the assistant, Dr. Harrison Mu, was out of network and sent the $117,000 bill. Insurance experts say surgeons and assistants sometimes share proceeds from operations, but Tindel's office says he and Mu do not. Mu's office did not respond to requests for comment.

The phenomenon can take many forms. In some instances, a patient may be lying on a gurney in the emergency room or in a hospital bed, unaware that all of the people in white coats or scrubs who turn up at the bedside will charge for their services.

Can't fight back

At times, a fully trained physician is called in when a resident or a nurse, who would not charge, would have sufficed. Services that were once included in the daily hospital rate are now often provided by contractors, and even many emergency rooms are staffed by out-of-network physicians who bill separately.

When insurers intervene in a particular case, they say they have limited ability to fight back. Insurance examiners "are not in the room on the day of surgery to see the second surgeon walk into the room or why they were needed," said Clare Krusing, a spokeswoman for America's Health Insurance Plans, an industry group. And current laws do not require hospitals that join an insurance network to provide in-network doctors, labs or X-rays, for example.

So sometimes insurers just pay - to protect their customers, they say - which encourages the practice.

When Drier complained to his insurer, the company cut a check to Mu for $116,862, the full amount.

When Drier agreed to surgery in December, he was not in a good position to bargain or shop around. Several weeks earlier, he had woken up to excruciating pain in his upper back. A scan showed that one of the disks that normally serve as cushions between vertebrae was herniated and pushing on a nerve. He was living on painkillers.